Method for improving continuously cast strands

ABSTRACT

Method of improving the structure of continuously cast strand by separating undesirable hot metal inclusions at locations spaced from cooling wall surfaces of a continuous casting mold and removing at least a portion of the superheat of molten metal internally of the shape being cast. Apparatus is provided for delivering hot metal subsurface to molten metal level within a continuous casting mold with a component of motion opposite to the direction of casting, initially confining such metal,and changing its direction of movement for separating undesirable inclusions. Apparatus is provided for introducing solid metal below the slag and molten metal surface into the high temperature zone.

United States Patent [1 1 Hill [ METHOD FOR IMPROVING CONTINUOUSLY CASTSTRANDS [75] Inventor: William P. Hill, Allison Park, Pa.

[73] Assignee: National Steel Corporation,

Pittsburgh, Pa.

[22] Filed: June 25, 1971 [21] Appl. No.: 156,818

4,521,192 Japan 164/57 Primary ExaminerR. Spencer Annear A ttorney-Shanley & ONeil [57] ABSTRACT Method of improving the structure ofcontinuously cast strand by separating undesirable hot metal inclusionsat locations spaced from cooling wall surfaces of a continuous castingmold and removing at least a portion of the superheat of molten metalinternally of the shape being cast. Apparatus is provided for deliveringhot metal subsurface to molten metal level within a continuous castingmold with a component of motion opposite to the direction of casting,initially confining such metal,and changing its direction of movementfor separating undesirable inclusions. Apparatus is provided forintroducing solid metal below the slag and molten metal surface into thehigh temperature zone.

9 Claims, 6 Drawing Figures STRAND TEMPERATURE SPEED Patented July 17,1973 3 Sheets-Sheet 1 FIG I INVENTOR WILLIAM P HILL 7 32 l I K ATTORNEYSPatented July 17, 197s 3 Sheets-Sheet 2 FEED RATE DRIVE COMPUTERCONTROLLER TEMPERATURE SHELL I THICKNESS STRAND CARBON CONTENT SPEEDFIG. 4

INVENTOR WILLIAM R HILL ATTORNEYS INVENTOR WlLLlAM P. HILL ATTORNEYSFIG. 5

3 Sheets-Sheet 3 A m f M M m no. a

1 l/ T l Patented July 17, 1973 METHOD FOR IMPROVING CONTINUOUSLY CASTSTRANDS This invention is concerned with improving the final structureof continuously cast strand. In particular this invention is concernedwith improving both surface characteristics and internal texture ofcontinuously cast strands by directional control of the discharge and bycontrol of the temperature of molten metal within a continuous castingmold. The invention is also concerned with increasing casting speeds incontinuous casting operations.

The invention will be described in an environment for continuous castingof steel. The ability to consistently produce continuously cast steelsuitable, as cast, for reduction to flat rolled product such as tinplatehad not been fully developed prior to this invention.

The problem is compounded by the need to cast steels which are killedsufficiently to avoid the violent reaction of rimmed steels in thecontinuous casting mold. Killing steel most commonly involves aluminumadditions. The formation of alumina results. Solidification of aluminaand other inclusions at and under the surface of the casting hasprevented achieving the surface quality required on the slabs, or othershapes, as delivered from continuous casters. However, it has beendiscovered that the problem is not merely a matter of surfaceinclusions. solidification of metal at the mold walls proceedssufficiently differently in relation to solidification centrally, thatunequal stresses are set up, cracks are produced, and breakouts canoccur. Slower casting rates have been tried in an attempt to avoidbreakouts but this apparently does not solve the problems associatedwith a thin shell on the strand as delivered from the mold.

Notwithstanding use of relatively slow casting rates, the driving forceand pressure of the molten metal, as introduced into the mold in theprior art, penetrates deeply into the casting, causing agitation andinternal piping in the cast product. Also the agitation against theshell being formed and the superheat of such incoming metal are factorsin preventing desirable shell thickness growth. This invention providesfor increasing shell thickness of a continuously cast strand within themold while increasing casting speeds over those previously available.

Significant contributions of this invention stem from systematically anduniformly regulating the movement of molten metal being dischargedcentrally within a continuous casting mold and controlling the superheatlevel of molten metal within the mold. The agitation caused bymechanical forces of the incoming metal and the separation of inclusionsfrom such metal within the mold are concentrated at a location spacedfrom the mold walls to increase both surface cleanliness and strandshell thickness.

The accompanying drawings will be used in presenting a more detaileddescription and bringing out other advantages of the invention. In thesedrawings:

FIG. I is a schematic elevational cross-sectional view of continuouscasting apparatus embodying the invention;

FIG. 2 is a schematic cross-sectional plan view of the apparatusembodying the invention;

FIG. 3 is a schematic elevational view, partially in cross section ofapparatus embodying the invention showing modified support structure;

FIG. 4 is a schematic elevational cross sectional view of apparatusembodying the invention showing another embodiment of support structure;

FIG. 5 is a plan view of apparatus embodying the invention showinganother embodiment of support structure and adjustment means, and

FIG. 6 is an elevational view, partly in section of the apparatus ofFIG. 5.

In carrying out the objects of the invention, a snorkel device, ofspecial configuration, is used to introduce molten metal in a particularfashion subsurface to the metal level within a continuous casting mold.In the inventive combination, a special, flow-through, sleeve structureis used to temporarily confine metal, effecting a change in direction ofmetal movement at the upper portion of the mold, spaced from the moldwalls.

Several differing types of snorkels can be investigated in priorpatents, for example in the U.S. patents to Junghans Nos. 2,224,303,2,225,414, and 2,243,425 and the patent to Mills et al., No. 3,517,726.Also other patents disclose suspended structures, other than snorkels,within a continuous casting mold; for example Canadian patent No.519,175 and U.S. Pat. No. 3,533,462. However, the prior art has notconsidered the particular problems undertaken nor the solutions providedby the present invention and none of the prior patents show theparticular structures and combinations of the present invention.

In the invention, as shown in FIG. 1, snorkel l0 interconnects tundish12 with continuous casting mold 14 providing an elongated passagebetween the two along the longitudinal axis of the snorkel. Stopper 16controls the flow of molten metal 18 from tundish 12 into suchlongitudinal passage.

Note that the flow of metal from snorkel 10, Le. the discharge of moltenmetal within the casting mold, is controllably directed in an upwarddirection. This controlled movement results from the orientation ofupwardly directed apertures, such as 20 and 22. Also note that metaldoes not flow from the snorkel axially; axially directed discharge isprevented by snorkel terminating end 26. The flow of metal fromapertures, such as 20 and 22, is upwardly and outwardly as indicated byarrows at 28 and 30. The introduction of molten metal and the removal ofstrand from the mold are controlled to maintain the desired molten metallevel in the mold.

Unusual advantages of the invention stem from the use of a confiningsleeve-like, open-ended box structure 32 in surrounding relationship tosnorkel 10. The coaction between the snorkel and the sleeve, combiningupwardly directed discharge and the confinement of metal spaced from themold walls while undergoing a change in direction of movement, helpsproduce the long sought surface quality in continuous casting. Thesleeve 32 acts as a trap for the undesirable inclusions in the metalbeing cast and keeps such inclusions from solidifying against the moldwalls. Also the agitation of the incoming metal is concentrated andessentially confined to the upper part of the mold within the finclusiontrap.

Note in the embodiment of FIG. 2 that snorkel l0 and the inclusion trapstructure 32 can be integral and that the cross-sectional configurationof sleeve '32 approximates the cross-sectional configuration of thecontinuous casting mold. Considering the configuration aspects, animportant teaching of the invention is that the peripheral spacingbetween the inclusion trap 32 and the casting mold 14 is selected so asto avoid freezing of molten metal along the molten metal meniscus 36between the two structures.

The molten metal discharged from the snorkel and being directed asindicated by arrows 28 and 30 will wash against the inner surfaces ofthe sleeve structure in an upward direction and be temporarily confinedwhile changing direction of movement within the sleeve. This inducedaction permits alumina and other inclusions to flow to the surfacewithin the confines of the inclusion trap structure.

Casting powder is added within the inclusion trap to assist in thisseparation and help form a slag layer 40 within the confines of sleeve32. Access to the upper end of the sleeve can be maintained to permitremoval of inclusion accumulations. Casting powder is also addedexternally of the sleeve to form a cover layer 41 between the inclusiontrap 32 and the mold walls. Both slag layers, internally and externallyof the sleeve structure 32, have the purpose of limiting heat radiationfrom the metal thereby helping to avoid a freeze over. Also, the laglayers help to prevent oxidation across the surface of the molten metal,assist in lubrication and assist in removing inclusions.

One outstanding advantage of the sleeve structure and the upward flow ofmetal confined within the sleeve structure spaced from the continuouscasting mold walls is the substantial elimination of the splashing ofmetal against the mold walls. As part of this contribution, theinvention substantially eliminates the freezing of undesirableinclusions against the chilled mold walls as well as freezingof metalwhich could cause scaling.

Significant in this regard is the opportunity, provided by the inventivestructure for metal to solidify to form the shell in the relatively calmarea between the inclusion trap and the mold walls. The agitation ofincoming metal at the mold walls in prior practice contributed tosolidification and accumulation of many of the inclusions against thecast surfaces as solidifying metal was washed away by the incomingmetal.

The strand shell, solidifying against the water cooled mold 14, is shownat 42 in FIG. 1. Substantially eliminated are the inclusions andinferior surface which had previously caused faults in product rolleddirectly from continuously cast strands unless extensive surfacescarfing and the like, are substantially reduced or eliminated by thepresent invention.

Another important benefit of the inventive sleeve arrangement is theprevention of agitation deep within the molten center of the strandpreviously caused by the downwardly directed kinetic energy, ferrostatichead, and depth of penetration of the molten metal stream. The unusualaspect of the invention is that this benefit is provided notwithstandingthe flow-through features of the sleeve maintained by the invention.

Considering this flow-through feature, note the absence of obstacles orbarricades preventing downward flow within the mold. The unusual aspectis that this flow-through feature is provided and, at the same time, themomentum and pressure of the metal being cast are dissipated in anupward direction so as to avoid the deep penetration which previouslyextended fifteen to twenty feet within the strand. With such deeppenetration pockets of superheated metal could exist deep within thecasting causing piping which would not heal.

Referring to FIG. 1, the molten metal flows downwardly within andoutwardly from the sleeve as indicated by arrows 44 and 46. A portion ofthe flowthrough metal rises around the outer surfaces of the sleeve andstarts the solidification process against the mold walls surrounding thesleeve. It is important that the shell solidification starts in thequiescent, relatively inclusion-free, area between the sleeve structureand the mold walls. There are several additional factors whichcontribute to the clean rim provided by the invention. Any inclusionswhich might escape the trap structure tend to rise to the surface and donot readily adhere to the metal shell which has been formed on the moldwalls. Any such alumina or similar types of inclusions moving againstthe sleeve is likely to adhere and accumulate on this refractorystructure.

In practice the snorkel and sleeve structures can be unitary as shown inFIG. 2. In this way both structures can be suspended from the tundish bythe snorkel sleeve and upper flange as shown in FIG. 1. Other supportarrangements can be used without impairing the inventive contributions.

In FIG. 3 the sleeve 50 is supported on the continuous casting mold 14by sleeve holders 52,53. The snorkel 54 is suspended from the tundish 12independently of the sleeve. The latter is connected to the mold 14 bybars such as 52 and S3 spaced about the sleeve and the mold so thataccess to the area between the sleeve and the mold is available foradding slagging powder, etc. With this type of structure the sleevewould oscillate if the mold oscillates, and its use may be restrictedunder certain circumstances. Molten metal flows axially downwardlythrough the axial passage of the snorkel 54 and upwardly from thesnorkel outlets as described earlier in relation to FIG. 1.

As is known, heat transfer in conventional continuous casting operationsoccurs substantially entirely through the mold walls by transfer of heatthrough the solidifying steel. As the steel solidifies and shrinks awayfrom the mold walls some thermal insulation occurs and the superheat inthe metal tends to keep the shell thickness from increasing. However,novel additional heat removal methods and means are provided by theinvention.

Included in the overall objective of the invention are improvements inthe control of casting speed. An important aspect of the inventivecombination which contributes to such purpose is the controlled additionof solid metal within the mold. Also, the location of the solid metaladdition is important to the overall objective of the invention. Optimumoperational efficiency and optimum effect from the solid metal additionare made possible by the means for introducing solid metal of thepresent invention.

Referring to HO. 3, sleeve 50 comprises longitudi nally extending wallsof refractory material of sufficient thickness to provide the strengthand durability required. Such sleeve walls are provdied with openings,such as 56 and 58, extending longitudinally throughout the length ofsuch peripheral walls. Through these longitudinally directed apertures,wire, rod, strand, web or the like, for example steel wires 60 and 62,which substantially fill the apertures within the sleeve walls, are fedinto the molten metal. It should be noted that such solid metal makesits first substantial contact with the molten metal internally of themold walls as the metal flows from the sleeve means. This is the ideallocation to remove superheat and to control the temperature of metal.Also freeze-up of metal within the apertures is avoided.

Steel wire, or the like, is selectively fed at a predetermined andcontrolled rate into the metal contiguous to the exit side of the sleeve50. The objective is to remove sufticient superheat from the metal toprovide for more uniform cooling across the strand, decrease erosion ofthe shell by incoming metal, and to increase the skin thickness of theslab leaving the mold. With steel, the steel added should preferablyhave a carbon content higher than the steel being cast in order tofacilitate dissolution.

The rate of feeding of the steel wire, or other shape, through thesleeve 50 is selected so as to obtain the desired solidification withinthe mold.

As brought out above, the sleeve means and the snorkel means coact withone another to bring about the special advantages enumerated. The sleevemeans serves an additional purpose of providing methods and means forincreasing heat removal from the molten metal within the mold at anoptimum location. This additional aspect of the present inventionfunctions in conjunction with the previously described coaction betweenthe sleeve means and the snorkel means by virtue of the double purposeof the sleeve means. As the description of the heat removal feature ofthe present invention proceeds it will be obvious that this function ofthe sleeve means can be carried out in the absence of the snorkel means.The apertures in the sleeve wall permit the addition of wire, rod, orthe like at 'a location to prevent the erosion of the shell by thesuperheat of the metal being added.

The present invention teaches the addition of solid metal at a preferredlocation subsurface to molten metal level in the high temperature zoneof the mold to remove heat internally. The total rate of heat removalcan be increased and, by this method, controlled more accurately forbest results. Adding solid metal, as taught, to a caster operating atconventional casting rates decreases the liquid core depth and the timerequired for complete solidification. Alternatively, casting speeds canbe proportionately increased or an intermediate casting speed can beselected. Melting of the wire is required, of course, for qualityreasons. Therefore in the continuous casting of steel, the carboncontent of the added solid steel is preferably increased above thecarbon content of the metal being cast, e.g. if the steel being cast hasa carbon content of about 0.05% C. then the steel wire can have aslightly higher carbon content, ranging up to about 0.1% C. This willinsure dissolution of the added solid metal in the casting and will notsignificantly change the'carbon content of the casting.

ln steel casting, the feeding of the wire into the superheated steelalso affects the solidification modes. Equiaxed grains tend to be formedand grow at a greater rate while the extent of the dendritic typegrowthwill tend to be suppressed.

Referring to FIG. 3, steel wire 60 can be fed from coil 66 eithermanually or by feed rate drive means 68. Several factors can affect therate of feed of the solid metal additive, for example, the desiredcasting speed, the optimum thickness of the shell 70 within the mold orupon exit from the mold, and uniformity of the shell thickness. Howevera dominant factor in controlling the feed rate of added solid metal isthe desired temperature level of metal within the mold after leaving theinclusion trap. Such temperature can be determined by a variety of knownsensors and measurement steps. Such measurement can be fed intocontroller 72 for use in controlling the feed rate of the solid metaladditive. The heat removal provided per unit weight of metal additivecan readily be determined by one skilled in this art. The heat removalrequired based on the feed rate of molten metal can also be readilydetermined. Controller 72 can be computer operated. Other data fed intocontroller 72 can be the carbon content for the steel being cast, shellthickness and the speed of the strand. Output of computer controller 72can include a signal for controlling solid metal feed rate, a signal foruse in selectively controlling casting speed, and the like. Suitablecomputer and control apparatus for carrying out such teachings of theinvention are available in the computer and electronic control art.

The optimum temperature for metal in the mold for particular castingspeeds and materials can be predetermined. Controlling the feed rate ofsolid metal, in either lbs/unit time or lbs/ton cast, manually or bycomputer, can be responsive to such temperature.

As a representative example in the casting of steels of the coordinatedcontrol taught by the present invention, attempts should be made toeliminate the superheat of the steel within the mold so as to arrive attemperatures such as the following for the designated plain carbonsteels:

Approximate Carbon Content Temperature 0.l0C 2,785F 0.20C 2,770F 0.40C2,745F 0.60C 2,720F 0.70C 2,700F

These temperatures are the desired approximate tem peratures within themold below the sleeve 32. Several thermocouples, e.g. inserted throughthe wall of sleeve 32 can be used to measure and obtain the averagetemperature at the desired location. Also, knowing the approximate heatlosses and the rate of casting, the temperature of the metal in thetundish can be measured and the amount of solid metal additive requiredto obtain the desired temperature within the mold can be calculated.

As shown in FIG. 2, solid metal additive apertures can be distributedabout the periphery of sleeve 32 at locations -87. Remaining aperturesinclude thermocouple sensing devices 92, 94 for measuring thetemperature of metal within the mold after exit from the sleeve. Aplurality of submerged thermocouples is used, distributed about the moldand the average temperature is obtained.

As stated, the temperature of metal in the mold can be calculated withaccuracy suitable for operation from a temperature measurement in thetundish taken with temperature means 96 shown in FIG. 3.

Suitable refractory materials for the snorkel means and sleeve meansdisclosed are well known in the art. Similarly, powder additives andslag forming materials to be added are well known in the continuouscasting art. The snorkel should be sealed where connected to thetundish, for example as shown at 97 in FIG. 3, so

as to avoid syphoning-of air into the metal and introduction of airbelow-the surface of the bath. If desired,

cover means (not shown) can be supported across the sleeve.

In FIG. 4 holding bracket means 98 is provided for supporting the sleevestructure. Bracket 98 is attached to tundish 100. In this embodiment thesnorkel 102 is also supported by tundish 100. Sleeve 104 is suspendedfrom tundish 100 by a series of spaced chains 106, 108, or othersuspension means permitting access to and visibility of the metal andslag surface within the sleeve.

FIGS. and 6 show an alternate embodiment of the invention providingindependent support via the tundish means for both a snorkel means andan inclusion trap means.

In the scissors jack type of linkage of FIGS. 5 and 6, linkage armsinterconnect tundish 110 and the inclusion trap means 112. Snorkel means114 is separately connected to the tundish.

As shown in FIG. 6, upper linkage arms 115 and 116 are pivotallyconnected to the tundish at brackets 117 and 118. The lower linkage arms119 and 120 are pivotally connected to the inclusion trap means 1 13 atring means 121 and 122. The junctures of the upper and lower linkagearms are interconnected by threadmounted sleeves 125 and 126 to threadedcrank arm 130. Crank mechanism 132 operates to raise and lower theinclusion trap means; the mechanical operation of such linkage means iswell known. The raised position of linkage arms is shown in dotted linesat 136.

The embodiment shown permits visibility of and access to the mold areafor making additions or raising and lowering of the inclusion trap. Alsoeach of the embodiments provides for solid metal additions through themold wall as described in relation to FIG. 3.

It is important that operational steps and dimensional aspects beselected for the slab or billet caster such that freezing of the metalacross the meniscus between the sleeve and the mold walls is avoided.The size and shape of strands cast vary so that the sleeve is selectedin relation to the mold size and product being cast to avoid suchfreezing. For example, when casting a 32 inch width slab ofapproximately 9 inch thickness the spacing of lateral ends between thesleeve and the mold walls may be about five inches at each end. Thisspace is determined by the factors mentioned. Spacing along each side iseffected by the minimum snorkel diameter required to avoid clogging orundue impedance to flow due to accumulation of alumina or the like. Ingeneral an overall outside diameter of about four inches is generallyrequired for large slab casting of steel.

In practice the inclusion trap means can be raised until after start ofthe cast. The inclusion trap can be preheated, in the preferred methodtaught, by being lowered slowly into the superheated metal following thestart of casting and proper mold level has been obtained. As the moldfills and withdrawal of the strand commences, the incoming-metal isintroduced subsurface to the metal level within the mold.

The inclusion trap means and snorkel means make unusual contributions inimproving surface characteristics without the use of the solid metaladditive teachings. Also a special coaction exists between the sleevecombination and the metal additive teachings since the location of thesolid metal additions taught by the invention helps to prevent theerosion of the shell by the superheated molten metal exiting from thesleeve.

The present invention is especially advantageous in the continuouscasting of steels suitable for sheets,

plate and the like, but has similar advantages in the casting of othersteels and metals. These advantages include elimination of surfaceinclusions and internal porosity, generally improving the quality ofproduct, increasing casting capacity, and reducing breakouts incontinuous casting operations.

In describing the invention apparatus has been set forth and methodsdescribed for reducing surface inclusions and improving internalcharacteristics of continuously cast strand by controllably introducingmolten metal into a continuous casting mold so as to be dischargedsubsurface to molten metal level in the mold with a component of motionopposite to the direction of casting, initially confining such metal andreversing the direction of flow of the metal to permit removal of themaximum amount of the metal impurities, and coordinating this operationwith, or optionally practicing separately, heat removal internally ofthe strand. While specific structures have been set forth it will bereadily understood that variations in such structures and materials willbe readily available to those skilled in the art based on the teachingsof the present application. Therefore it is understood that the scope ofthe invention should not be limited to specific structures shown but isto be determined by reference to the appended claims.

I claim:

1. Method for improving the structure of continuously cast strandcomprising the steps of introducing molten metal into a continuouscasting mold with such molten metal being introduced subsurface tomolten metal level within the mold and being discharged within the moldso as to have a component of motion opposite to the direction ofmovement of continuously cast strand,

initially confining the molten metal as introduced into the continuouscasting mold within an openended inclusion trap means located within thecontinuous casting mold spaced from the mold walls such that a change indirection of movement of the molten metal occurs causing separation ofundesirable inclusions frorn'the molten metal within the inclusion trapmeans, and

removing superheat from molten metal internally of the continuouscasting mold by introducing solid metal into such molten metal.

2. The method of claim 1 in which the solid metal is introduced throughwall means of the inclusion trap means in the form'of continuous-lengthtype wire, rod, web or the like.

3. The method of claim 1 in which the molten metal is steel ofpredetermined carbon content and the solid metal added has a highercarbon content than the molten metal being cast. I a

4. The method of claim 3 in which the solid metal added is used tocontrol the temperature of molten metal within the continuous castingmold at a temperature determined at least in part by the carbon contentof the steel being cast.

5. The method of claim 1 including the step of controlling casting speedin coordination with solid metal additions.

6. Method for reducing surface inclusions and improving the internalstructure of a continuously cast steel strand comprising the steps ofintroducing molten steel into a vertically oriented continuous castingmold with the molten steel being introducted subsurface to molten metallevel within the mold and being discharged within the mold so as to havea component of motion opposite to the direction of strand casting,

initially confining and changing the direction of movement of the moltensteel as introduced into the continuous casting mold within an openended inclusion trap means having a cross sectional configurationapproximating that of the continuous casting mold but spacedsufficiently from the mold walls to avoid freezing molten steel betweenthe inclusion trap means and the mold walls, such change of direction ofmolten metal providing for removal of undesirable inclusions remote fromthe mold walls within the inclusion trap means,

adding slagging ingredients to aid in removing inclusions from themolten metal within the inclusion trap means, and

removing superheat from the molten steel internally of the mold byintroducing solid steel in wire, ribbon, or similar form into the moltensteel as delivered from the inclusion trap means into the continuouscasting mold.

7. Method for improving the final structure of continuously cast strandcomprising the steps of introducing molten metal into a continuouscasting mold with such molten metal being introduced subsurface tomolten metal level within the mold and being discharged within the moldso as to have a component of motion opposite to the direction ofmovement of continuously cast strand,

initially confining the molten metal as introduced into the continuouscasting mold within an openended inclusion trap means located within thecontinuous casting mold spaced from the mold walls causing a change indirection of movement of such molten metal and separation of inclusions,

adding slagging ingredients to the surface of the mo]- ten metal withinthe inclusion trap means, and maintaining inflow of molten metal to thecontinuous casting mold and withdrawing solidifying strand from the moldso as to maintain molten metal within the mold at a desired level.

8. Method for improving surface characteristics and internal structureof continuously cast strands comprising the steps of removingundesirable inclusions from molten metal as introduced into a continuouscasting mold, such removal occurring remote from cooling wall surfacesof such mold by constraining initial movement of molten metal asintroduced within an open ended sleeve means spaced from cooling moldwall surfaces, and

adding solid metal to molten metal within the continuous casting mold toremove superheat from such molten metal centrally of the mold.

9. The method of claim 8'in which solid metal addi tives are controlledresponsively to the temperature of molten metal in the mold.

1. Method for improving the structure of continuously cast strandcomprising the steps of introducing molten metal into a continuouscasting mold with such molten metal being introduced subsurface tomolten metal level within the mold and being discharged within the moldso as to have a component of motion opposite to the direction ofmovement of continuously cast strand, initially confining the moltenmetal as introduced into the continuous casting mold within anopen-ended inclusion trap means located within the continuous castingmold spaced from the mold walls such that a change in direction ofmovement of the molten metal occurs causing separation of undesirableinclusions from the molten metal within the inclusion trap means, andremoving superheat from molten metal internally of the continuouscasting mold by introducing solid metal into such molten metal.
 2. Themethod of claim 1 in which the solid metal is introduced through wallmeans of the inclusion trap means in the form of continuous-length typewire, rod, web or the like.
 3. The method of claim 1 in which the moltenmetal is steel of predetermined carbon content and the solid metal addedhas a higher carbon content than the molten mEtal being cast.
 4. Themethod of claim 3 in which the solid metal added is used to control thetemperature of molten metal within the continuous casting mold at atemperature determined at least in part by the carbon content of thesteel being cast.
 5. The method of claim 1 including the step ofcontrolling casting speed in coordination with solid metal additions. 6.Method for reducing surface inclusions and improving the internalstructure of a continuously cast steel strand comprising the steps ofintroducing molten steel into a vertically oriented continuous castingmold with the molten steel being introducted subsurface to molten metallevel within the mold and being discharged within the mold so as to havea component of motion opposite to the direction of strand casting,initially confining and changing the direction of movement of the moltensteel as introduced into the continuous casting mold within an openended inclusion trap means having a cross sectional configurationapproximating that of the continuous casting mold but spacedsufficiently from the mold walls to avoid freezing molten steel betweenthe inclusion trap means and the mold walls, such change of direction ofmolten metal providing for removal of undesirable inclusions remote fromthe mold walls within the inclusion trap means, adding slaggingingredients to aid in removing inclusions from the molten metal withinthe inclusion trap means, and removing superheat from the molten steelinternally of the mold by introducing solid steel in wire, ribbon, orsimilar form into the molten steel as delivered from the inclusion trapmeans into the continuous casting mold.
 7. Method for improving thefinal structure of continuously cast strand comprising the steps ofintroducing molten metal into a continuous casting mold with such moltenmetal being introduced subsurface to molten metal level within the moldand being discharged within the mold so as to have a component of motionopposite to the direction of movement of continuously cast strand,initially confining the molten metal as introduced into the continuouscasting mold within an open-ended inclusion trap means located withinthe continuous casting mold spaced from the mold walls causing a changein direction of movement of such molten metal and separation ofinclusions, adding slagging ingredients to the surface of the moltenmetal within the inclusion trap means, and maintaining inflow of moltenmetal to the continuous casting mold and withdrawing solidifying strandfrom the mold so as to maintain molten metal within the mold at adesired level.
 8. Method for improving surface characteristics andinternal structure of continuously cast strands comprising the steps ofremoving undesirable inclusions from molten metal as introduced into acontinuous casting mold, such removal occurring remote from cooling wallsurfaces of such mold by constraining initial movement of molten metalas introduced within an open ended sleeve means spaced from cooling moldwall surfaces, and adding solid metal to molten metal within thecontinuous casting mold to remove superheat from such molten metalcentrally of the mold.
 9. The method of claim 8 in which solid metaladditives are controlled responsively to the temperature of molten metalin the mold.